Work machine

Abstract

Provided is a work machine capable of regenerating a return hydraulic fluid from a hydraulic actuator while preventing a drag loss of a regeneration hydraulic motor and a hydraulic pump from increasing and preventing the regeneration efficiency of the regeneration hydraulic motor from decreasing. A controller 100 computes a required regeneration hydraulic motor revolution speed from a displacement of a regeneration hydraulic motor 13 and a regeneration flow rate of the regeneration hydraulic motor, computes a required first hydraulic pump revolution speed from a displacement of a first hydraulic pump 15 and a target assist flow rate of the first hydraulic pump, and selects a greater one of the required regeneration hydraulic motor revolution speed and the required first hydraulic pump revolution speed as a target revolution speed of an electric motor 14.

The invention claimed is: 
     
       1. A work machine comprising:
 a first hydraulic actuator; 
 a second hydraulic actuator; 
 a regeneration hydraulic motor that is driven by a return hydraulic fluid discharged from the first hydraulic actuator; 
 a first hydraulic pump mechanically coupled to the regeneration hydraulic motor; 
 an electric motor mechanically coupled to the regeneration hydraulic motor; 
 a second hydraulic pump that delivers a hydraulic fluid for driving the first hydraulic actuator or the second hydraulic actuator; 
 a junction line that allows a hydraulic fluid delivered by the first hydraulic pump to join a hydraulic fluid delivered by the second hydraulic pump; 
 a first operation device that directs an operation of the first hydraulic actuator; 
 a first operation amount sensor that detects an operation amount of the first operation device; 
 a second operation device that directs an operation of the second hydraulic actuator; 
 a second operation amount sensor that detects an operation amount of the second operation device; 
 a first pressure sensor that detects a pressure in the first hydraulic actuator; 
 a second pressure sensor that detects a pressure of the second hydraulic pump; and 
 a controller configured to receive signals of the first operation amount sensor, the second operation amount sensor, the first pressure sensor, and the second pressure sensor and output a control command to the electric motor, 
 the controller being configured to: compute a regeneration flow rate and a regeneration power of the regeneration hydraulic motor from the operation amount of the first operation device and the pressure in the first hydraulic actuator; compute a pump power of the second hydraulic pump from the operation amount of the second operation device and the pressure of the second hydraulic pump and set a smaller one of the regeneration power and the pump power as an assist power of the first hydraulic pump; and compute a target assist flow rate from the assist power and the pressure of the second hydraulic pump, wherein 
 the controller is configured to:
 compute a required regeneration hydraulic motor revolution speed from a regeneration hydraulic motor displacement and the regeneration flow rate, the required regeneration hydraulic motor revolution speed being a required revolution speed of the regeneration hydraulic motor, the regeneration hydraulic motor displacement being a displacement of the regeneration hydraulic motor; 
 compute a required first hydraulic pump revolution speed from a first hydraulic pump displacement and the target assist flow rate, the required first hydraulic pump revolution speed being a required revolution speed of the first hydraulic pump, the first hydraulic pump displacement being a displacement of the first hydraulic pump; and 
 select a greater one of the required regeneration hydraulic motor revolution speed and the required first hydraulic pump revolution speed as a target electric motor revolution speed, the target electric motor revolution speed being a target revolution speed of the electric motor. 
 
 
     
     
       2. The work machine according to  claim 1 , wherein
 the regeneration hydraulic motor is a variable displacement hydraulic motor, and 
 the controller is configured to control the regeneration hydraulic motor displacement according to the pressure in the first hydraulic actuator. 
 
     
     
       3. The work machine according to  claim 1 , wherein
 the first hydraulic pump is a variable displacement hydraulic pump, and 
 the controller is configured to control the first hydraulic pump displacement according to the pressure of the second hydraulic pump. 
 
     
     
       4. The work machine according to  claim 1 , wherein
 the regeneration hydraulic motor is a variable displacement hydraulic motor, and 
 the controller is configured to control the regeneration hydraulic motor displacement according to the target electric motor revolution speed and the regeneration flow rate. 
 
     
     
       5. The work machine according to  claim 1 , wherein
 the first hydraulic pump is a variable displacement hydraulic pump, and 
 the controller is configured to control the first hydraulic pump displacement according to the target electric motor revolution speed and the target assist flow rate.